Tubelab Simple SE with big honkin' Edcors?

[rknize]

Originally posted by tigrine
Hi Rknize,
When you use the EL34 what is the value of the cathode resistor ?
What is the B+ of your amp ?

By the way, your amp look very very nice!

The lowest setting is about 564 ohms. B+ is around 460 with this arrangement.

Thanks!

[rknize]

Originally posted by HEADinaJAR
A little different approach on my chassis. I got the 17"x10" plate drilled all the holes and bent a 90` 2 " from either end. But...... I may have messed up the bends. Ended up having to beat it with a hammer. My brother in-law the retired plumber just got rid of all his sheet metal bending equipt. Now to see if the hammertone paint will cover the hammering.

It will to a certain extent. I'd try to get it as flat as possible. How it turns out depends a lot on how it is applied and the humidity and all that. It looks like what it is is two types of paint that are not quite compatible, so the upper layer fish-eye's on the lower layer and you get a pitted effect.

[rknize]

So I've been having a lot of fun tube-rolling with this amp. It's more fun than a fixed bias amp because I don't have to fiddle with fine bias adjustments. Just click the bias knob and go. Another fun aspect is that the differences between different kinds of tubes are less subtle than in PP amp. So for anyone who cares, these are my observations of the tubes I like the most and the settings that I have available to me:

- SED EL34: in triode mode with no CFB, these sound fairly close the Tubelab SE with 300Bs in terms of detail. They are the best that the amp can do for listening to classical and some other live recordings I have. Biasing them hotter does not improve the sound. The extra power that they have over the TSE with 45s is handy for rock, so those live concerts sound good. While they do have slightly less bass than "bigger" tubes, it's not that noticeable on my more sensitive speakers. This may be helped by the 5000 ohm primaries on the OPTs. They can rock in UL+CFB, but not as well as....

- SED KT88 and Tung-Sol 6550 (Reflektor): these tubes can rock and roll. They lack in fine details for classical and other "critical" listening, but for casual-but-loud rock/pop/trance listening they are great. When I have the house to myself and flip all the switches (CFB+UL+SS rectifier), rock-concert volumes are easily attained. Not as loud as the Dynaco can get, but ear-damaging volumes without annoying distortions can be achieved. Fun to do once in a great while (though bad for your ears).

- EH KT90: these are probably my overall favorite tubes in this amp. These are those odd-looking tall tubes with all the extra fins on the plates. I am quite surprised at the detail they have as triodes at 70-80mA. I did a bunch of "critical" listening with these at normal volume and went back and forth between the EL34s and these. Other than a bit more bass extension, I could not *really* tell the difference in terms of details. Maybe a little...I dunno. The sound stage was awesome and I think these tubes have a more pleasant midrange than the SED EL34s. The KLF-10s are 2-way and are somewhat lacking in the midrange. I generally prefer a laid-back midrange, but these speakers go a little to far for me. These tubes brought some of that back and it made me happy.

The KT90s do *look* like big EL34s, but I didn't think they would actually sound like that. I expected them to sound like the other big Reflektor tubes that seem the same to me, but these are different. What's really great is that like the KT88s, I can flip the switches on these tubes and rock at high volume. They sound awesome at 100mA like this. 324ohms is the lowest bias resistance setting I have, but I am wondering if these tubes want even more bias. The plates are long and with all those fins I think they can take it. Obviously, tube life is a trade-off here.

I've had these KT90s for many years for a large PP amp that I never built. I tried them once or twice in the Dynaco ST70, but they don't really sound any different than any other 6550/KT88 I put in there. I don't see them around too much anymore and I don't often hear anyone talking about them. TubeDepot still lists them, though. Anyone else have any experience with these? Am I just hearing things?

Anyone who is considering building this amp setup for UL should seriously consider CFB as well. I tried UL without CFB many times. It always got louder, but the treble tended to become too dominant over the midrange and bass compared to when CFB was enabled and the volume increased instead. The input/driver stage seems to have the necessary headroom to push the outputs into cutoff even with the feedback. This surprised me, as I figured that these big honkin' Edcors wouldn't really benefit much from the local feedback. I didn't try UL-only much with my other, less sensitive speakers. Maybe it's just the horns in the KLF-10s that need to be reeled-in a bit.

Even when running at 100mA per tube for hours on end, this power transformer barely gets warm. It has plenty of capacity and gives just the right B+ for anything you could want to do with this amp with any tube except the 6V6 types (which need a lower B+). Even if you don't want to spend the money of the Edcor OPTs, I can't recommend this power transformer enough over the Hammond or Allied.

Anyway, despite my earlier reservations, this is a great amp. I hope my ranting earlier hasn't turned anyone off to building one.

[oldmanStrat]

Thanks for the very detailed listening report Russ - I'm always curious to hear what people find good and not so good about any particular setting or tube.

I'm definitely no audiophile, but my observations are similar to yours. The Kt88's are the loudest tube in the bunch, the EL34's nice, but not enough punch. And my current favorite is the 6l6 - it has just enough boom, and sounds cleaner than the Kt88.

KT90... thats a new one. I may have to check out those too.

Does anyone have a convenient way of organizing tubes? I'm starting to get quite a few of them...

This amp is definitely a keeper. But I've decided that I'm going to build a Tubelab SE too. Gotta see what the fuss is all about with DHT...

[nic6paul]

I too have been enjoying this amp for the past week or so. Now I am in search of a nice pair of 6l6gcs and a pair of kt88. I was thinking of picking up the EH kt88s but I wasnt too sure about the 6l6gcs. I acquired a pair of Black plate RCAs but when I used them at higher volumes one of the speakers started to distort and I am assuming that one of the tubes is going bad. The guy that gave them to me wasn't promising they would work but he thought they would. Either way you cant resist free. Any one have any recommendations on a 6l6gc set? I have the coke bottles which I have actually been using since I built this thing. I also have a pair of E34l JJs but I really miss the lower note detail that these seem to lack.

[oldmanStrat]

I bought mine from AES - just the cheapo chinese 6L6GC's. I have no idea if spending more would produce better sound

One interesting thing with these tubes - the plate is glowing red in spots. I double checked the table George has on the cathode resistor (mine is 560) and it should be right in the middle of the possible selections. I don't think there is an issue, but perhaps a better quality 6L6GC wouldn't do this...

[HEADinaJAR]

Great post Russ. All I've tried is the set of JJ E34L's. I did get e pair of used Tung Sol Kt-88's and a 5U4 rect. off ebay cheap but no chance to try them out.

I wanted to warn people about what I foolishly did. Iprinted out Georges PDF of the Simple SE PCB and used it as a template to drill the holes in my chassis. Guess what.....my printer printed the PDF about a quarter inch smaller than actual (it's done this before, come to think of it). I should have checked this first, before I drilled. Also I didn't leave enough room for my volume control. So... I have... another chassis plate coming.

[Ty_Bower]

Originally posted by HEADinaJAR
I wanted to warn people about what I foolishly did. Iprinted out Georges PDF of the Simple SE PCB and used it as a template to drill the holes in my chassis. Guess what.....my printer printed the PDF about a quarter inch smaller than actual. I should have checked this first, before I drilled.

Good tip. I always design my entire chassis layout on the PC, then print out a template. I have a couple of printers from which to choose. One of them gives more accurate results than the others. After I print, I setup the transformers, sockets, switches, etc right on top of the print. At this point I usually spot errors or maybe I just don't like the spacing of something. Markup the drawing, edit the template, print again.

[rknize]

Originally posted by HEADinaJAR
Great post Russ. All I've tried is the set of JJ E34L's. I did get e pair of used Tung Sol Kt-88's and a 5U4 rect. off ebay cheap but no chance to try them out.

I wanted to warn people about what I foolishly did. Iprinted out Georges PDF of the Simple SE PCB and used it as a template to drill the holes in my chassis. Guess what.....my printer printed the PDF about a quarter inch smaller than actual (it's done this before, come to think of it). I should have checked this first, before I drilled. Also I didn't leave enough room for my volume control. So... I have... another chassis plate coming.

Yes I had this same problem, but I have had it before so I checked it before using it as a template. In the case of George's amps, the SSE and TSE, it was Adobe Acrobat Reader that was the problem. The PDF contains an exported letter-side page containing the layout. When you go to print, Acrobat automatically scales it down so that it fits within the margins of your print setup/printer which is also letter sized. There is an option in the print dialog not to scale. You might get a waning about printing out of the margins, but nothing is there...just white space of the embedded page.

[oldmanStrat]

Originally posted by HEADinaJAR


I wanted to warn people about what I foolishly did. Iprinted out Georges PDF of the Simple SE PCB and used it as a template to drill the holes in my chassis.

I nearly did the same thing - but I'm very wary of how my pdf reader prints images (ie not to scale). Probably wouldn't be a problem if I was using Adobe - pretty sure there is a button to press that says don't scale to page - but my Linux app isn't quite as fully featured...

Luckily George was very quick with sending the actual PCB to me so when I compared the print to the original I saw the problem.

Having a print of the right scale is very useful though - especially when locating all the holes with a punch. There isn't a center hole for the tubes in the PCB !

Originally posted by Ty_Bower

After I print, I setup the transformers, sockets, switches, etc right on top of the print.

I do this too. I call it the paper doll exercise. It's amazing how many little things you can catch doing this.